The efficiency of abrasive blasting is to a considerable extent determined by the energy-related factors of abrasive particles, namely, speed of ejection, uniform density of the generated gas/abrasive mixture flow and its temperature, and the possibility of its onstream regulation in the course of the process. That is why the bulk of publications consider optimization of the route “nozzle gun—means for air-abrasive mixture generation” to be a predominant factor in determining the quality and the capacity of the abrasive blasting.
Normally, two modes of abrasive blasting of surfaces are employed, namely, blasting using cold air/abrasive jet, and thermal abrasive blasting. In the first case, the flow of abrasive is being generated using high-velocity compressed air jet incoming directly from a compressor or another source, the main acting agent at that being the kinetic energy of the abrasive particles excited by this jet (cf., e.g., SU 0221534, Pichko, 01.08.1968; SU 1703425 A1, Marchuk et al., 07.01.1992; WO 99/39874, Seitter et al., 12.08.1999). In the second case, the device comprises a means for generating of high-temperature gas jet and its mixing with abrasive medium flow, usually located in the nozzle gun (cf., e.g., SU 0344977, Meerovich et al., 14.07.1972; WO 88/05711, Krivorozhsky ore and mining institute, 11.08.1988; U.S. Pat. No. 5,607,342, Evdokimenko et al., 04.03.1997; WO 01/81044 A1, Danilov et al., 01.11.2001; EP 1155781 A1, Thermo Blast International SA, 21.11.2001; UA 36316 A, Shpaket et al., 16.04.2001).
The common constituent parts of all surface abrasive blasting devices, irrespective of temperature mode of processing, are the nozzle gun and the mixer of abrasive with the carrier gas (air), connected to each other with a flexible hose. The mixer for abrasive is connected to the vessel for abrasive through a batcher. The feeding is carried out from a receiver connected to a compressed air source. The overpressure is also created in the abrasive tank, for which purpose the latter is also connected to the compressed air source for generating motion of the abrasive flow (cf., e.g., U.S. Pat. No. 5,947,800, Fring, 07.09.1999).
In the invention WO 88/05711 the nozzle gun of the device for surface thermal abrasive blasting comprises a body equipped with delivery pipes for liquid fuel and compressed air, a combustion chamber with radial through-holes being installed along its direct axis. The input to the combustion chamber is equipped with a swirl for swirling of the fuel blend. The nozzle for discharging of the high-temperature jet is installed at the output of the combustion chamber, the output orifice of gas/abrasive jet being located in its critical section. Liquid fuel and compressed air feeding pipes are located radially.
There is also a known jet device for thermal abrasive blasting comprising a body, which further comprises a combustion chamber with a prechamber, air flow swirlers located concentrically, a spray burner and a fuel blend homogenizer. The device comprises also a cooling jacket and a replacement nozzle embodied as a confuser and a choke tube conjugated on a curved surface. The jacket is connected to the chamber through radial holes (RU 2158197 C1, Danilov et al.; WO 01/81044).
There is also a known jet device for thermal abrasive blasting comprising an annular radial choice tube for fuel feeding to the combustion chamber providing for buildup of a protection film on its walls (RU 2163864 C2, OAO PO “Energoprom-Stroyzashchita”, 10.03.2001).
The device (RU 2167756 C2, Kostritsa et al., 27.05.2001) comprises a pipeline of abrasive/air mixture with a swirler located around it. It further comprises a body, a regeneration pipe, a nozzle, a combustion chamber formed by the flue tube with radial holes and a swirler. Integrated in the case is a mixing chamber connected to fuel feeding channel and communicating with the oxidant feeding channel and the swirler. The end of the abrasive mixture feeding pipeline is located between the last row of radial holes and the input section of the nozzle. Fuel ignition is performed with an electric spark plug.
The jet device described in EP 1555781 is featured by a cylindrical body comprising concentrically located air cooling chamber formed by the sleeve and the solid wall fastened to each other forming a maze. The combustion chamber possesses a perforated wall and a tubular element for air/abrasive feeding equipped with feeding pipes for gaseous oxidant, liquid fuel and gas/abrasive mixture, respectively. It further comprises a swirler embodied as spiral channels for gaseous oxidant feeding for creation of the fuel blend, orifices for fuel input connected to the liquid fuel feeding pipe located between the combustion chamber perforated wall at its blank end and a tubular element. The output nozzle embodied as a Laval nozzle is equipped with a means for axial displacement and fastening to the cylindrical body. The ignition spark plug communicates with the combustion chamber.
Means for metering of abrasive input to the mixer to provide for uniform abrasive density in the jet device flow are described in a number of publications (cf., e.g., U.S. Pat. No. 5,433,653, Friess, 18.06.1995; EP 0694367 A1, Kegler, 31.01.96; EP 0950469 A2, Rickling, 20.10.1999). The publication (EP 0950469 A2, Rickling, 20.10.1999) describes the design of a blast valve using a movable choke remotely controlled by a pneumoengine. In the device described in another publication (EP 0694367, A1, Kegler, 31.01.96) the discharge orifice of the abrasive vessel comprises a regulating needle installed on a lever, the position of which is remotely controlled by a jack with a reducing gear. Such means for metering and transporting of an abrasive material to a mixer and further to a nozzle gun could only be employed for specially desiccated and prepared abrasive media with no caking trends. Otherwise, whirlwind formation and violation of abrasive feeding to the gas flow could occur, which makes the processing uncontrollable, hence irreproducible. Such violation of the technology would play the most essential role in case of thermal abrasive blasting due to uncontrollable abrasive feeding to the work area.
The analysis of the cited publications demonstrates the described devices to implement the modes of only either “cold” or “hot” abrasive jets. At the same time, there exists the demand in an abrasive blasting device that would provide for operation in both modes and would possess enhanced efficiency in both power requirements and operational features, namely, convenience of control, reduced consumption of abrasive, tool life in the thermal abrasive blasting mode, and stability of the abrasive jet. Of no less importance for a hand-held jet device are its weight and dimensions—these should be rather small.